1. Field of the Invention
The invention relates generally to a method for the removal of paint from metal surfaces, such as aircraft surfaces, and more particularly to a paint removal method that involves directing a pressurized stream of a ceramic particle/liquid mixture upon the painted surface.
2. Description of the Prior Art
The removal of paint from aircraft surfaces is an important, periodic operation associated with both inspection and maintenance procedures on military and commercial equipment. The paint is removed both to enhance the inspection of underlying metal and composite surfaces as well as part of the routine maintenance associated with degrading paint quality.
Until recently, chemical paint removal options were more or less standard practice. With the growing concern for environmental quality and waste remediation and control, the casual use and disposal of paint removing chemicals is no longer acceptable. Consequently, thermal and mechanical removal methods which minimize environmental impact and permit collection of waste products have come under consideration.
Paint removal means have included directing solid abrasive particles in an air jet toward the painted surface as disclosed in U.S. Pat. No. 5,092,084 to Schlick. A problem associated with this type of paint removal method lies in the collection of the abrasives and the separated paint. Painstaking collection means are typically employed which could involve running the contaminated abrasives through separators and screens. An example of such a collection scheme is disclosed in U.S. Pat. No. 4,773,189 to MacMillan et al. Aside from drawbacks in the collection of the contaminated abrasive materials, these types of paint removal methods create a large amount of dust and generate heat on the painted surface that may result in thermal degradation.
Waterjet and water plus abrasive hydrojet options are particularly attractive for automated large surface area paint stripping considerations because the presence of water serves to minimize dust, cool the surface (to prevent thermal degradation), and assist in the collection of waste product (depainting residue). In addition, cutting versions of these systems are already widely used in a variety of industries.
Despite proven deployment concepts and significant environmental advantages, hydrojet techniques involve very high localized energy levels which could affect material properties (redistribute favorable residual stresses, distort fastener hole alignment, etc.). In addition, without a good water collection system, waste product collection can be difficult and effective disposal options nil. Also, conventional hydrojet systems do not offer an option (excluding on/off control) for adjusting the amount of abrasive in the water stream.
Clearly, a system which can be adjusted to efficiently remove paint from multiple layers yet not impact the underlying surface is required as well as a waste product collection system which can effectively and reliably collect and sort virtually all paint residue for subsequent disposal.